The present invention relates to extension bars for connecting a mold ejector plate to a press ejector plate in an injection molding apparatus and in particular to extension bars which are adjustable in length.
In a conventional molding apparatus, a molded part is produced by injecting mold material into a cavity formed between a stationary and a movable mold half mounted to a mold press. The stationary mold half is mounted on a front stationary platen of the mold press and the movable mold half is mounted to a movable platen which is generally slidably mounted on tie-rods extending from the front stationary platen to a rear stationary platen of the mold press. The movable platen is hydraulically advanced toward and away from the front stationary platen during a mold cycle to move the movable mold half between a closed and open alignment with the stationary mold half.
Mold material is injected into the mold cavity when the movable mold half is positioned in the closed position relative to the stationary mold half. Once the molded part has set, the movable mold half is separated from the stationary mold half, and the molded part is then ejected from between the two mold halves using an ejector assembly.
A typical ejector assembly comprises a plurality of ejector pins, which are connected to a mold ejector plate slidably mounted relative to the movable mold half. The mold ejector plate is connected to a press ejector plate by extension bars or tie in bars. The ejector pins are slidably mounted within the movable mold half in bores which open into the mold cavity. The ejector pins are advanceable between a retracted position within the bores to an extended position wherein a portion of each ejector pin extends into the mold cavity for ejecting the molded part out of the cavity.
The mold ejector plate is typically mounted within a chamber in the moveable mold half. The mold ejector plate is mounted in the chamber to permit it to slide toward and away from the mold cavity. The extension bars extend through aligned holes in the movable platen and a rear wall of the movable mold half and connect the mold ejector plate to the press ejector plate.
In ejecting the molded part from the mold, the movable platen is first advanced away from the front stationary platen to pull the movable mold half away from the stationary mold half. After the moveable mold half has separated from the stationary mold half and advanced to a fully open position, the press ejector plate is hydraulically advanced forward to advance the mold ejector plate forward relative to the moveable mold half and to advance the ejector pins from a retracted to an extended position thereby ejecting or separating the molded part from the moveable mold half.
The molded part then typically falls from between the stationary and moveable mold halves. The press ejector plate is then retracted hydraulically and the mold halves are advanced to a closed alignment and the cycle is repeated.
The stationary and moveable mold halves are removably securable to the mold press such that different molds may be interchangeably connected to the mold press to permit efficient utilization. In changing out a mold, the moveable mold half must be disconnected from the moveable platen and the extension bars must be disconnected from the mold ejector plate contained within the moveable mold half. The new moveable mold half must then be connected to the moveable platen and the extension bars must then be connected to the mold ejector plate.
The optimum length of the ejection stroke for the ejector pins will vary from mold to mold depending on differences in the size and shape of the part to be molded. In addition, the length of the extension bars may need to be adjusted during the life of the mold to accommodate wear to the mold. In existing systems, mold press operators typically use extension bars specifically machined to the desired length and must continuously machine extension bars to fit different molds and presses.
There remains a need for an extension bar or tie-in bar for connecting a mold ejector plate to a press ejector plate which is readily adjustable in length and adapted to expedite mold changes and set-up.